In prior art devices for parallel combining RF power transistors, an even number of transistors, generally four, are combined by using a symmetrical transmission line matching network. A typical example of a four transistor combining network is disclosed in U.S. Pat. No. 3,784,932, issued Jan. 8, 1974 and entitled "Parallel Transmission Line Matching Network for Connecting Together a Plurality of RF Amplifier Transistors". In general, these prior art combining networks are relatively expensive because of the use of an additional transistor and the associated extra circuitry.
Some work has been done in the past to combine three semiconductor devices using three equal length lines generally configured so as to radiate from a single combining point. However, these are unsatisfactory because of the extreme length of the lines, which causes a physical problem (placing the lines) and an electrical problem (as will be explained in more detail presently).